1. Field of the Invention
The present invention generally relates to evaporative cooling processes. It especially relates to indirect evaporative cooling processes that employ an array of heat transfer plates to create channels through which a pre-cooled gas (e.g., air) and an evaporative liquid (e.g., water) are directed in order to carry out said processes.
2. Discussion of the Background
Indirect evaporative cooling processes can be used to remove undesired heat from various industrial, commercial and domestic facilities. For example, such processes can be employed to remove undesired heat from electrical power plants, oil refineries, chemical production plants, air conditioning systems and so on. Indirect evaporative cooling processes seek to take advantage of the fact that, if the temperature of a gas (such as air) entering such a process is lowered prior to its coming into direct contact with an evaporative liquid (such as water), the lowered gas temperature will produce a lowered wet bulb temperature of that pre-cooled gas. Consequently, the temperature of an evaporative cooling liquid that comes into contact with such a relatively cooler gas stream also will be lowered. If this concept is carried to its ideal limits, the temperature of the incoming gas could be lowered to a wet bulb temperature that approaches its, relatively lower, dew point temperature.
U.S.S.R. Patents 641260 and 690271 to Maisotsenko describe evaporative cooling apparatus having a dry side channel and a wet side channel that are separated by a heat exchange plate. An air stream entering the dry side channel is pre-cooled by passing it downward along the heat exchange plate when it is in a cooled condition. This downward flowing stream of air can be cooled without raising its humidity. This air stream is then directed around the lower edge of the heat exchange plate. Thereafter, the air stream is directed upward (in a generally counter-flow direction relative to the downward flow direction of the incoming air) along the opposite, wet side of the heat exchange plate. This wet side of the heat exchange plate also serves as a wall of the wet side channel.
Meanwhile, water is directed downwardly in the wet side channel and especially along a continuously wetted side of the heat exchange plate. Some of this descending water evaporates into the pre-cooled, counter-flowing air stream as it passes upward through the wet side channel. That is to say that the evaporated water has taken up its heat of vaporization and become a component of the upwardly flowing air stream. This evaporation process cools the remainder of the descending water as well as the wet side surface of the plate. This cooled condition of the wet side surface of the plate will be transmitted through the body of the plate to its dry side. This, in turn, will cause heat to be removed from the incoming air stream that is flowing downwardly through the dry side channel. This pre-cooling of the air in the dry side channel (without raising that air's humidity) also causes the air to have a relatively lower wet bulb temperature. Ideally, this lower wet bulb temperature will approach the air's dew point temperature. Processes of the type described in the Maisotsenko patents have come to be known as “indirect evaporative cooling processes”.